There is substantial interest in the petroleum industry for converting heavy hydrocarbonaceous feedstocks to lower boiling liquids. The hydrogenation of heavy oil is used for increasing the up-grading of heavy hydrocarbons. According to such a process, heavy hydrocarbons are converted to lighter products and mid-distillate liquids of lower boiling points. Heterogeneous catalysts, such as sulfides of Co, Mo or Ni on an aluminium oxide support, are utilized.
High molecular weight components of the crude oil, adsorbed by the catalyst surface, plug the pores and active sites of the catalyst, and therefore gravely reduce the activity of an hydrogenation reaction. The asphaltene and organometallic compounds of the crude oil are separated, deposited on the catalyst surface and deactivate the catalyst. The heavier the hydrocarbon is, the shorter the catalyst lifetime becomes. One requirement of such processes is to always hold a high partial pressure of hydrogen.
U.S. Pat. No. 4,637,870 describes a hydrogenation refinery method, in which a phosphorus and molybdenum containing catalyst is added to an aqueous solution. During this process, phosphoric acid changes to phospho-molybdic acid. This solution is mixed with hydrocarbons to get the primary solution of the catalyst. The resulting primary solution is dehydrated and sulfidized, added to feedstock (heavy oil or heavy residue), and then introduced into the reactor for the hydrogenation reaction to start. During the mentioned process, commercial phospho-molybdic acid of a P/Mo atomic ratio of 0.08 up to 1/0.1 up to 1 is used. Phospho-molybdic acid, for reducing the resulting coke, is added, said ratio in the solution should be 0.12 up to 1/0.45 up to 1.
The drawback of this method is the high amount of produced coke, difficulties with preparing the catalyst and adding the catalyst to the feedstock before entering the reactor. Still further, the used catalyst is very expensive and that makes the method uneconomical.
U.S. Pat. No. 4,659,454 refers to a hydrocracking method for heavy oil in which over 75% of the fractions the boiling points of which are over 400° C. are mixed with 5-50% of distillation fractions with boiling points of 150-400° C. Compounds of IV, V, VI, VII, and VIII transition metal elements that are present in this mixture will decompose as a result of being heated. The acidic zeolite catalyst solid is added to the feed in an amount equal to 0.1 to 10 weight percent of the feed. Said process was performed at 250-500° C., under a pressure of 25-50 MPa in mixing or plug flow reactor with a liquid hourly space velocity of 0.1-10 h−1.
Application of high pressures in said method (more than 25 MPa) and the consequent need to special equipments, the relatively low production of light hydrocarbon fractions and also the lack of a good solution for catalyst regeneration and separation of metals present in feedstock are the drawbacks of this method.
Another method is disclosed in the FR 2,631,631, in which the hydrogenation process is performed at 430° C. by using the sulfides of transition metals, suspending the feedstock.
The catalyst of said method is prepared as follows.                Metallic compounds of VIIB, VIIB, and VIII elements, such as Mo, phosphomolybdic acid and a salt of phosphomolybdic acid are mixed with the asphaltene and organic polysulfides containing feedstocks.        The resulting mixture is heated in the presence of hydrogen gas and under a pressure of 0.5-20 MPa and temperature of 260-450° C.        The resulting concentrated catalyst is added to the feedstock.        
The difficulties with preparing the catalyst, the necessity of application of polysulfides, which makes the technology both difficult and expensive, and the lack of a suitable solution for catalyst regeneration are the problems of the said method.
U.S. Pat. No. 5,039,392 altered the above described method by using sulfur as the sulfidizing element in the preparation of the primary concentrated catalyst solution.
That method includes:
The dispersion of the aqueous catalyst solution in the hydrocarbon solution, dehydrating, sulfidizing, the addition of the resulting mixture to feedstock and introducing the second resulting mixture into the reactor for the reaction to start.
The amount of catalyst in said method is about 50-300 ppm, the produced coke (solid product) is about 2% and at least 1.8% by mass.
The high amount of produced coke, difficulties with catalyst preparation due to the dehydrating and vulcanizing steps are problems of said method.
WO 93/03117 describes the hydrogenation conversion of heavy hydrocarbons to lower boiling point products at 343-515° C., using hydrogen (50-5000 psig) and adding concentrated catalyst, wherein said concentrated catalyst is prepared as follows:                The primary catalyst solution is prepared by mixing hydrocarbon fractions of boiling points of higher than 570° C. with aqueous solutions of metal compounds of II, III, IV, V, VIIB, VIIB and VIII metals of the Periodic Table, in a way that the amount of metal in the said feedstock is from 0.2 to 2 percents by mass.        By heating the primary catalyst prepared according to the first step (without adding hydrogen) is sulfudized at 275-425° C. with elemental sulfur as the sulfiding agent.        
Preparation of concentrated catalyst under special conditions and according to an unnecessarily sophisticated step, application of expensive phosphomolybdic acid and lack of a solution for the problem of catalyst regeneration are disadvantages of this method.
U.S. Pat. No. 6,004,454 presents another method for hydrocracking of heavy oil and residuum, namely by using a dispersing-type catalyst that is dispersed in the feedstock.
Said catalyst contains (2-15) mass percents of Mo, (0.1-2) mass percent of Ni and (0.1-3) mass percents of phosphorous. The oxides or salts of Mo and Ni are dissolved in water to prepare the catalyst.
Unprocessed oil and primary raw material (heavy residue) are mixed with said catalyst, the mixture is heated and it enters the reactor. The hydrocracking reaction is performed in 380-460° C. and under a pressure of 10-15 MPa.
Said catalyst is added in an amount that the concentration of said active metals reach 150-1500 ppm. The outlet of distillation fractions in this process is about 70% by mass, and is mostly coke free.
The low amount of distillation fractions outlets, high cost of the method due to the high flow of the process and lacking a suitable method for catalyst separation are disadvantages of this method.
RU 2,146,274 refers to a method for the conversion of raw heavy hydrocarbons.
According to this method the catalyst is evenly distributed through the feedstock. The catalyst is directly made in the reaction zone from the emulsion formed by mixing the feedstock with the aqueous solution containing molybdate. Emulsion of the catalyst (aqueous solution) in oil is prepared in advance. Gas containing hydrogen is fed to contact the prepared emulsion which results in hydrogenation of the mixture. Light fraction containing 70% distillate reacts at a boiling temperature of up to 500° C. and is refined by hydrogenation. Reaction products are divided into distillate fractions with boiling temperature of up to 350° C. and residuals with more than 350° C. In this case, all of the residuals with boiling temperature of more than 350° C. are burned for catalyst regeneration and separation of metals existing in the feedstock.
The drawback of this method is the low amount of light hydrogenation products. Environmental and economic indexes of this method are low because a considerable amount (1-40)% of the hydrogenation residue, which contain valuable fractions, are lost when heated more. Another disadvantage of this method is that the residues with boiling points of more than 350° C. return to said hydroconversion process, while it contains viscose materials like coke, asphaltenes and the spent catalyst, reducing the yield of the process.